Question 1048639
.
tan(-15°) = tan(15°) = {{{sqrt(2-sqrt(3))/sqrt(2+sqrt(3))}}} = {{{2-sqrt(3)}}}.


See the lesson 

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=https://www.algebra.com/algebra/homework/Trigonometry-basics/Trigonometric-functions-of-half-argument-Examples.lesson>Trigonometric functions of half argument - Examples</A> 

in this site.